Motor device



111$ 9 7 M. MORRISON 2,415,022

IO'IOR DEVICE Filed July 23, 1943 2 Sheats-Sheet '1 jllmzhrijforrzism Jan. 28, 1947.

Filed July 28, 1943 Parallel resonant circuit rdbge/ eagle 01' lead nzik respeei 2a feed bdcl current M. MORRISON uo'rox DEVICE 2 Sheets-Sheet 2 oliage and zhgaedam offlal'allel resonantaa'rezgzt sfesamrwe fr-ezaeracj diafre aenc and m alar speed .flngle of lay with respect Z0 feed back aur'nent Mani/0rd flkrrzis'ang.

5,, faarm Patented Jan. 28, 1947 UNITED STATES PATENT OFFICE 6 Claims.

The invention relates to electric motor devicesv in which the rotor is required to run at a predetermined, highly accurate fixed speed.

Among the objects of the invention are; to provide operable from a, direct current source, an electric motor having high degree of constancy of speed, to provide such a motor withspeed characteristics which are independent, over large ranges of variation, of the voltage of the current source, to provide easy and convenient means of changing the value of the fixed speed, and 'to provide a simple and efiective method of forcing the rotor of such a, motor to firmly synchronize with minute injections of alternating currents of a frequency at, or near, the operating frequency of the rotor.

This invention may be employed in many instrument and apparatus applications for the generation of precise audio frequencies, precise timing in optical systems, in the construction of measuring and testing devices, for the synchronous operation of signal devices as well as for further and other applications which will be obvious upon reading the specification and claims hereoi. By the employment of this invention small, compact and light motor mechanisms may be constructed with speed regulations better than 0.01% and the present invention is applicable to devices and apparatus requiring this constancy of speed.

The invention will be more fully understood from the following description when read in connection with the accompanying drawings, Fig. 1 01' which is acircuit diagram of an arrangement embodying the principles of the invention in simple formi'or clearness in explaining the basic operating characteristics of the invention;

' Fig.'2 is a side view illustrating in some detail to the elements illustratedin the elevation shown rotor illustrative of the term "rotor phase angle in connection herewith as used herein.

Referring to Fig. 1, which is an alternating current motor which may,

synchronously with an applied alternating voltage. This motor may be of the inductor type with salient poles, a direct current field type with in practice, be any one .01 the many'types which can be made to operate Fig. 4 is a, fragmentary drawing of part of the I a device unsuitable In the embodiment shown in Fig. 1, i employ The field member 2 nated speed control can be obtained but only at a very high apparatus cost and with an excessive amount of weight.

ave a very high precision of constancy, the instantaneous frequency value may and often does vary badly, thus making such for certain types of precision work where a complete absence of hunting is essential.

In the employment of my invention there is a complete absence of hunting, which will be hereinafter be more fully described.

The oscillatory system H is connected through feed-back circuits l3 and [4 to the plates of the twin triodes 9 which are, as before stated, connected push-pull to the windings 4 and 5.

These feed-back circuits l3 and I4 are constructed along the linesof feed-back circuits used in resistance stabilized audio frequency oscillators. That is, the condensers employed are large in capacity for the frequency employed and the resistors are very high in comparison with the plate resistance of the twin triodes. The impedance of these feed-back circuits is such that the voltage developed across the oscillatory system ll does not sensibly affect the value of the feed-back current. The resistors of the feed-back circuit are also sufficiently high, that the current through this feed-back circuit is substantially of the form and phase of the voltage across the windings 4 and 5 of the motor I.

With such characteristics the feed-back circuit may be referred to as having a resistance current-limiting characteristic. In other words, the form and phase of the current through these resistors is such as is produced by a pure resistance, the impedance of the condensers and the oscillatory circuit being so small in comparison that they contribute no sensible effect upon the circuit impedance. Two feed-back circuits l5 and I6 are also provided so that when switches l1 and .18 are closed, alternating current from source l9 may be fed into the oscillatory system H with or without feed-back current,

Referring to Fig. 1, I may provide an electrical load at the position so designated and I may introduce a condenser 20 by closing the switch 2|. By so doing I provide tuning for the motor winding which is useful in some applications.

Referring to Fig. 2, there is illustrated on the shaft 22 a metal disc 23 which may be caused to revolve in thefield of a permanent magnet 24 producing an eddy current brake as a load on the device which is referred to hereinafter as mechanical load.

Since the feed-back circuits I3 and I4 have purely a resistance characteristic, the current follows the form, amplitude and phase of the-voltage across terminals I and 8, but the voltage developed across parallel oscillatory system II will rise and fall according to the resonance curve of the oscillatory system, as a function of the frequency, as is well understood by those skilled in the art.

In Fig. 3 is the general form of the voltage curve as a function of the frequency with the resonance value indicated, as is commonly illustrated. Also,

the phase angle of this voltage curve is illustrated in Fig. 3. Since the current lags the voltage for resonance frequency in such a system,'the voltage then leads the current over similar range of frequencies. The phase angle curve is slightly displaced depending upon the Q of the circuit.-

It will be appreciated from Fig. 3 that oscillatory system I l produces a grid-control which not only gives amplitude variations as function of the voltage but phase angle variations.as a funcj tion of the voltage.

The current through windings 4 and 5 has a phase displacement with the voltage at terminals win triodeS.

The phase angle of theplate-current of the own characteristics rather 100% increase in voltage.

. windings.

twin triode 9 is of course affected by the electrical load, so designated, tuning 20 so illustrated, or by mechanical loading, as described in Fig. 2. However, the phase angle between the voltage and the current in the windings t and 5 are not affected by these added parameters.

The speed at which the rotorfi operates depends upon the phase angle, between the voltage and current in the windings 4 and 5 and the mechanical loading on the rotor, different speeds having difierent phase angles.

. Referring to Fig. 4, the angular phase position between the rotor and the current in windings 4 and 5 is indicated by the letter 0. The more the mechanical loading the larger the angle 0, this lagging position accounting for the increased torque demand caused by the increased loading, as is well understood by those familiar with the art of synchronous motor operation.

In some respects this motor operates like a synchronous motor, but its speed is determined by its than that of an external generator.

Its speed characteristics being determined mainly by the-phase angle, between the voltage and the current in its windings and the mechanical loading, means that the motor will must a speed, and only at that speed,.corresponding' to the phase angle of the current supplied to the motor, with referenc to the voltage across its Of course, such a motor above its operating speed and allowed to coast back into the operating speed, but the speed at which it continues to operate always depends mainly upon these two factors above stated.

If the motor is brought up to a certain high speed and allowed to coast it falls to a frequency at which the oscillatory system II will provide the right phase angle for the requirements.

The voltage has very little effect upon the speed of the motor, even sometimes over a range of As a matter of fact, within operating ranges the voltage is so unrelated to the speed of the motor that it is Possible to make adjustments so that the motor slows up with increased voltage and speeds up with a decrease in voltage.

In the ordinary synchronous motor, the motor is attempting to operate through a somewhat elastic system with a fixedsource of frequency and the elasticity of this system together with the inertia of the parts constitute a more or less electromechanical oscillatory system in the rotor itself, commonly known as hunting.

This motor has no tendency whatever to hunt as there is no elastic connection between the rotor of the motor and its source of supply, this relation is hired and rigid and one follows the other perfectly, and therefore there can be no hunting.

In a well designed motor having a good strong direct current field the embodiment of my invention produces a comparatively high torque motor with a high apparatus efficiency and high electrical efilciency and is entirely unlike small synchronous motors with their comparatively high current inputs and low torques, to say nothing of the instability due to hunting.

The applicant does not limit himself to the structure shown in the described embodiment. The limitations of the invention are set forth in the claims hereunder.

What I claim is: 1. An alternating-current motor system comhas to be brought up prising amotor having stator to supply driving energy to said rotor; a source of. direct-current power subject to voltage fluctuations, a capacitance-inductance parallel oscillatory circuit having an independent oscillating period to fix the altemating-current Irea stator, a rotor and an electromagnetic field-winding surrounding said electromagnetic field-winding surrounding said stator to supply driving energy to said rotor; a source of direct current power subject to voltage v fluctuations, a capacitance-inductance parallel quency of'said energy, an electronic discharge tube having a grid-control circuit and receiving plate-circuit power from said source, said plate circuit including said winding, said grid-controlcircuit including said oscillatory circuit, an en,- ergy iced-back circuit from said plate circuit to said oscillatory circuit, and said feed-back circuit including an impedance member to stabilize said oscillating period under operation with said voltage fluctuations.

2. An alternating-current motor system comprising a motor having a stator, a rotor and an electromagnetic field-winding surrounding said stator to supply driving energy. to said rotor; at

oscillatory circuit having an independent oscilfeed-back circuit including a resistance member source of direct-current power subject to voltage fluctuations, a capacitance-inductance parallel oscillatory circuit having an independent oscillating period to flxthe altemating-current frequency of said energy, an electronic discharge tube having a predetermined plate resistance and a grid-control circuit, said tube receiving platecircuit power from said source, said plate circuit including said winding. said grid-control circuit including said oscillatory circuit, a feedback circuitfrom said plate circuit to said oscillatory circuit, and said feed-back circuit including an impedance member having ahigher resistance than said'plate resistance to stabilize said oscillating period under operation with said voltage fluctuations.

3. An alternating-current motor system comprising a motor having a'stator, a rotor and an electromagnetic field-winding surrounding said stator to supply driving energy to saidrotor; -a source of direct-current power subject to voltage fluctuations, a capacitance-inductance parallel oscillatory circuit having an independent oscillating period to flx the alternating-current frequency of said energy, said oscillatory circuit having a predetermined ohmic impedance at res- 'onance, an electronic discharge tube having a grid-control circuit and receiving plate-circuit .power from said source, said plate circuit includcillatory circuit is dependent upon said oscillating period and substantially upon said oscillating period only. I

4;. An altemating-current motor system comprising a motor having a stator, a rotor and an feed-back current the voltage across said os-' having a higher ohmic impedance than that of said oscillatory circuit at resonance, 'and said" ohmic impedance of said reed-back circuit being higher than said plate impedance, whereby said oscillating period is stabilized under operation with said voltage fluctuations.

5. An alternating-current motor system comprising a motor having a stator; a rotor and an electromagnetic field-winding having a predetermined inductance surrounding said'stator to supply driving energy to said rotor; a source of direct-current power subject to voltage fluctuations, a capacitance-inductance parallel oscillatory circuit having a substantially constant oscillating period to flx the alternating-current frequency of said energy, an electronic discharge tube having agrid-control circuit and receiving plate-circuit power from saidsource, said plate circuit including said winding, said grid-control circuit including said oscillatory circuit, an energy feed-back coupling circuit from said fieldwinding to said oscillatory circuit, and means in -euit having an independent oscillating period to flx the alternating-current frequency of said energy, an electronic discharge tube having a gridcontrol circuit and receiving plate-circuit power from said source, said plate circuit including said winding, said grid-control circuit including said oscillatory circuit, an energy feed-back circuit from said plate circuit to said oscillatory circuit,

and said feed-back circuit includingan impedance member to stabilize said oscillating period under operation with said voltage fluctuations, whereby said periodic motion is frequency stabilized by said oscillatory circuit.

MONTFORD MORRISON. 

